Supplemental Financial Information (Supplemental Financial Information) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Supplemental Financial Information [Line Items]
Unbilled revenue	$ 33.0	$ 43.3
Customer receivables	69.6	56.4
Amounts due from partners in jointly owned stations	11.4	16.0
Other	7.8	6.0
Provision for uncollectible accounts	(0.9)	(0.8)
Total accounts receivable, net	120.9	120.9
Fuel and limestone	52.7	72.2
Plant materials and supplies	35.0	34.9
Other	2.4	2.0
Total inventories, at average cost	90.1	109.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Supplemental Financial Information [Line Items]
Unbilled revenue	33.0	43.3
Customer receivables	67.7	54.1
Amounts due from partners in jointly owned stations	11.4	16.0
Other	9.0	6.9
Provision for uncollectible accounts	(0.9)	(0.8)
Total accounts receivable, net	120.2	119.5
Fuel and limestone	52.7	72.2
Plant materials and supplies	33.8	33.7
Other	2.3	2.1
Total inventories, at average cost	$ 88.8	$ 108.0